<style>
  #star-six {
    width: 0;
    height: 0;
    border-left: 50px solid transparent;
    border-right: 50px solid transparent;
    border-bottom: 100px solid red;
    position: relative;
  }
  #star-six::after {
    width: 0;
    height: 0;
    border-left: 50px solid transparent;
    border-right: 50px solid transparent;
    border-top: 100px solid red;
    position: absolute;
    content: "";
    top: 30px;
    left: -50px;
  }
  </style>
  <body>
  <div id="star-six"></div>
  </body>